The invention relates to a process for making poly(trimethylene terephthalate) (xe2x80x9c3GTxe2x80x9d) crimped staple fibers suitable for yarn and other textile applications, to staple fibers, and to yarns and fabrics made from the staple fibers.
Polyethylene terephthalate (xe2x80x9c2GTxe2x80x9d) and polybutylene terephthalate (xe2x80x9c4GTxe2x80x9d), generally referred to as xe2x80x9cpolyalkylene terephthalatesxe2x80x9d, are common commercial polyesters. Polyalkylene terephthalates have excellent physical and chemical properties, in particular chemical, heat and light stability, high melting points and high strength. As a result they have been widely used for resins, films and fibers.
Polytrimethylene terephthalate (xe2x80x9c3GTxe2x80x9d) has achieved growing commercial interest as a fiber because of the recent developments in lower cost routes to 1,3-propane diol (PDO), one of the polymer backbone monomer components. 3GT has long been desirable in fiber form for its disperse dyeability at atmospheric pressure, low bending modulus, elastic recovery and resilience.
In many textile end-uses, staple fibers are preferred over continuous filament. These may include staple spun yarns for apparel fabrics, nonwoven materials, and fiberfills and battings. The manufacture of staple fiber suitable for these end uses poses a number of special problems, particularly in obtaining satisfactory fiber crimp, essential for downstream processing such as carding, and in providing a fiber with sufficient toughness (breaking tenacity and abrasion resistance) to produce staple spun yarns with sufficient strength for knitting and weaving for apparel end uses. In the case of 2GT, which is a widely used staple fiber in cotton systems processing as well as in fiberfill and nonwovens applications, these problems are being met by the fiber producers through improvements in polymerization chemistry and optimized fiber production. This has led to improved spinning, drawing and annealing processes tailored to the production of high performance 2GT fibers. There is a need for an improved 3GT staple fiber process which generates fibers with suitable processability in commercial mills employing carding and garnetting processes. The solutions to these problems developed over the years for 2GT or 4GT fibers frequently do not apply to 3GT fibers because of 3GT""s unique properties. These needs for tailored fiber properties in a typical 3GT staple yarn spinning process are further described below.
Downstream processing of staple fibers is typically done on cotton systems equipment. This process includes several steps, many of which are done at high speeds and subject the fibers to a significant amount of abrasion, placing demands on the fiber tensile properties. For example, the initial step is fiber opening, which is often done by tumbling the fibers on motorized belts which contain rows of pointed steel teeth for the purposes of pulling and separating large group of fibers. The opened fibers are then conveyed via forced air and, typically, are then passed thorough networks of overhead ductwork or chute feeders. The chute feeders feed the card, a device which separates the fibers and spreads them into a sheet-like layer, which is then fed into a series of rolls containing combing teeth at high speeds. The carded material is then either processed as a web into nonwoven fabrics or fiberfill applications, or is converted into a sliver for conversion into spun yarns. If converted to a sliver, it is then drawn at high speeds to increase uniformity. The draw process reduces the linear density, defined as weight per unit length, typically by a factor of 5 or 6. The drawn sliver is then spun into a yarn. Staple yarn may be spun from the drawn sliver by a number of commercial methods. These include ring spinning, open-end spinning, air jet spinning, and vortex spinning. All of these methods involve high speed twisting of the fibers, and passage of the yarn under tension over contact surfaces (e.g. guides and eyelets) during wind-up of the final yarn.
There are two major criteria for acceptable fibers in the above spun yarn process. The first is that the fibers must be suitable for making yarns of a fineness preferred for fabric and apparel applications. Since by definition, a staple yarn is composed of a series of short discontinuous fibers held together solely by twist and fiber-to-fiber friction, a certain minimum number of fibers, typically 100-180 fibers, are required in the cross section of the textile yarn to give it strength and continuity. This has the effect of limiting the range of the fiber denier per filament (dpf), and restricts the practical range of denier useful to make textile yarns to approximately 3 denier per filament and below. There is in principle no lower limit, but the carding process described above does not perform properly below about 0.8 denier per filament, making the overall practical denier range about 0.8 to about 3 denier per filament (about 0.9 to about 3.3 dtex) for spun yarns. Nonwovens typically utilize about 1.5 to about 6 dpf (about 1.65 to about 6.6 dtex) staple fibers. Higher denier fibers may be required for non-textile applications such as fiberfill, which utilize about 0.8 to about 15 dpf (about 0.88 to about 16.5 dtex) staple fibers.
The second condition is that the fibers must possess a critical set of physical properties to pass through the process with excellent efficiency (minimal fiber damage, nep formation, and various stoppages), while making a yarn, nonwoven fabric, or fiberfill material with sufficient strength for the desired textile end uses. With staple yarns it is especially important they have sufficient strength for knitting and weaving, and sufficient uniformity that they do not cause streaks and unevenness during dyeing and finishing.
For spun yarns containing synthetic fibers, one of the most critical parameters is fiber strength, defined as tenacity or grams of breaking strength per unit denier. It is particularly important in the case of low denier filaments, such as 1 to 3 denier per filament. In the case of 2GT, fiber tenacities of 4 to 7 grams per denier (gpd) are obtainable with low denier filaments. However, in the case of 3GT, typical tenacities are below 3 grams per denier in the low denier region. These fibers with only a few grams of breaking strength are not desirable for staple downstream processing.
There is a need for 3GT staple fibers with tenacities over 3 grams per denier which can be processed into an acceptable staple yarn via spinning techniques such as ring spinning, open end spinning, air jet spinning or vortex spinning. Another important property is the crimp take-up, which is important both for processing the staple fibers and for the properties of textile and fiberfill products made from the staple fibers. The crimp take-up measures the springiness of the fiber as imparted by the mechanical crimping process, and thus affects its handling characteristics such as downstream processing.
While commercial availability of 3GT is relatively new, research has been conducted for quite some time. For instance, British Patent Specification No. 1 254 826 describes polyalkylene filaments, staple fibers and yarns including 3GT filaments and staple fibers. The focus is on carpet pile and fiberfill. The process of Example 1 was used to make 3GT fibers. It describes passing a filament bundle into a stuffer box crimper, heat setting the crimped product in tow form by subjecting it to temperatures of about 150xc2x0 C. for a period of 18 minutes, and cutting the heat-set tow into 6 inch staple lengths.
EP 1 016 741 describes using a phosphorus additive and certain 3GT polymer quality constraints for obtaining improved whiteness, melt stability and spinning stability. The filaments and short fibers prepared after spinning and drawing are heat treated at 90-200xc2x0 C. This document does not teach a process for making a high tenacity crimped 3GT staple fiber.
JP 11-107081 describes relaxation of 3GT multifilament yarn unstretched fiber at a temperature below 150xc2x0 C., preferably 110-150xc2x0 C., for 0.2-0.8 seconds, preferably 0.3-0.6 seconds, followed by false twisting the multifilament yarn. This document does not teach a process for making a high tenacity crimped 3GT staple fiber.
JP 11-189938 teaches making 3GT short fibers (3-200 mm), and describes a moist heat treatment step at 100-160xc2x0 C. for 0.01 to 90 minutes or dry heat treatment step at 100-300xc2x0 C. for 0.01 to 20 minutes. In Working Example 1, 3GT is spun at 260xc2x0 C. with a yarn-spinning take-up speed of 1800 m/minute. After drawing the fiber is given a constant length heat treatment at 150xc2x0 C. for 5 minutes with a liquid bath. Then, it is crimped and cut. Working Example 2 applies a dry heat treatment at 200xc2x0 C. for 3 minutes to the drawn fibers.
U.S. Pat. No. 3,584,103 describes a process for melt spinning 3GT filaments having asymmetric birefringence. Helically crimped textile fibers of 3GT are prepared by melt spinning filaments to have asymmetric birefringence across their diameters, drawing the filaments to orient the molecules thereof, annealing the drawn filaments at 100-190xc2x0 C. while held at constant length, and heating the annealed filaments in a relaxed condition above 45xc2x0 C., preferably at about 140xc2x0 C. for 2-10 minutes, to develop crimp. All of the examples demonstrate relaxing the fibers at 140xc2x0 C.
All of the documents described above are incorporated herein by reference in their entirety.
None of these documents teach 3GT staple fibers suitable for textile applications or a process for making them.
The invention is directed to a process of making a polytrimethylene terephthalate staple fibers, comprising:
(a) providing polytrimethylene terephthalate,
(b) melt spinning the melted polytrimethylene terephthalate at a temperature of 245-285xc2x0 C. into filaments,
(c) quenching the filaments,
(d) drawing the quenched filaments,
(e) crimping the drawn filaments using a mechanical crimper at a crimp level of 8-30 crimps per inch (3-12 crimps/cm),
(f) relaxing the crimped filaments at a temperature of 50-120xc2x0 C., and
(g) cutting the relaxed filaments into staple fibers having a length of about 0.2-6 inches (about 0.5-about 15 cm).
The temperature of the relaxation is preferably about 105xc2x0 C. or below, more preferably about 100xc2x0 C. or below and most preferably about 80xc2x0 C. or below. Preferably, the temperature of the relaxation is about 55xc2x0 C. or above, more preferably about 60xc2x0 C. or above.
Preferably, the relaxation is carried out by heating the crimped filaments in an unconstrained condition.
In one preferred embodiment, the drawn filaments are annealed at 85-115xc2x0 C. before crimping. Preferably, annealing is carried out under tension using heated rollers. Preferably, the resultant staple fibers have a tenacity of at least 4.0 grams/denier (3.53 cN/dtex) or higher. Preferably, the resultant staple fibers have an elongation of 55% or less.
Preferably, the staple fibers are 0.8-6 denier per filament. In one preferred embodiment, the staple fibers are 0.8-3 denier per filament.
The crimp take-up (%) is a function of fiber properties and is preferably 10% or more, more preferably 15% or more, and most preferably 20% or more, and preferably is up to 40%, more preferably up to 60%.
In another preferred embodiment, the process is carried out without annealing. Preferably, the resultant staple fibers have a tenacity of at least 3.5 grams/denier (3.1 cN/dtex).
The invention is also directed to a polytrimethylene terephthalate staple fiber of 0.8 to 3 denier per filament having a length of about 0.2 to 6 inches (about 0.5 to about 15 cm), a tenacity of 3.5 grams/denier (3.1 cN/dtex) or more and a crimp take-up of 10-60%, containing 8 to 30 crimps per inch (about 3 to about 12 crimps/cm), prepared without annealing.
The invention is further directed to a 0.8 to 3 denier per filament polytrimethylene terephthalate staple fiber having a tenacity of 4.0 grams/denier (3.53 cN/dtex) or higher. Such fibers can have tenacities up to 4.6 grams/denier (4.1 cN/dtex) or higher. Preferably, they have an elongation of 55% or less.
In addition, the invention is directed to textile yarns and textile or nonwoven fabrics. The described fibers may also be used for fiberfill applications.
Using the processes of this invention, it is possible to prepare staple fiber and yarn of superior tenacity, softer fabric hand, increased fiber softness, superior moisture transport properties, improved pilling performance and increased stretch and recovery. The preferred fabrics have fuzzy pills (as opposed to hard pills), which results in less pill sensation.
The invention is also directed to blends of the fibers of the invention and cotton, 2GT, nylon, acrylates, polybutylene terephthalate (4GT) and other fibers. Preferred are yarns, nonwoven, woven and knitted fabrics comprising fibers selected from the group consisting of cotton, polyethylene terephthalate, nylon, acrylate and polybutylene terephthalate fibers.
The invention is also directed to a process of preparing a polytrimethylene terephthalate staple fiber having a desirable crimp take-up comprising (a) determining the relationship between denier and crimp take-up and (b) manufacturing staple fibers having a denier selected based upon that determination.